Yes, the barrel seems shorter than a standard model, the whole gun seems slimmer than the standard model and it looks like the artist also drew an additional "hammer" at the back end of the gun despite the luger doesn't have a hammer like most guns (those two "circles" on the side of the gun is the "hammer"/thing you pull to seem like a badass: *clicky-ty-clack*).

Yeah, the fact that its ejection port is on the side rather than on top makes no sense...for a luger. The people who drew this anime had no idea how guns work. When the gun is finally used, we see the toggle circles are just cosmetic, and the slide cycles on each trigger pull even when out of ammo as if the slide and trigger were directly connected.